docs: def retrieve(self, *args):
          """Get a value previously .store(...)'d.
  
          Needs at least five arguments. The -1th is the tick
          within the turn you want,
          the -2th is that turn, the -3th is the branch,
          and the -4th is the key. All other arguments identify
          the entity that the key is in.
  
          """
          ret = self._base_retrieve(args)
          if ret is None:
              raise HistoryError("Set, then deleted", deleted=True)
          elif ret is KeyError:
              raise ret
          return ret